STENT

Abstract: A stent shaped as a three-dimensional body which is formed by interlaced threads (1) arranged in multistart turns of a helical line. The threads (1) are arranged in at least two groups (2 and 3) of the helical turns featuring opposite senses of helix. The stent ends are established by sections (5) where the turns of one helical line merge into those of the other helical line, said sections appearing as a single length of the thread (1).

Description: Technical Field The present invention relates in general to medicine and more specifically to surgery and can find predominant application for endoreconstruction of blood vessels and other hollow organs and structures of the human body. The invention also enables the reconstruction of perforating lesions to be carried out. Background Art Modern medicine is capable of reconstructing blood vessels, ducts and perforating lesions of human organs, using special framework-type devices named stents. Use of stents makes it possible to restore the natural function of an defected anatomical structure without having to rely on direct operative interference techniques. In order to attain high-quality reliable endoprosthesizing said devices must possess a number of definite properties. First and foremost, stents must provide unobstructed motion of body fluids through the implanted structure without deteriorating metabolic processes in tissues. Such stents must be rigid enough to withstand the pressure exerted by the walls of blood vessels and body cavities, to provide uniform pressure distribution over the surface being prosthesized, and the same time possesses elasticity. Moreover, the stent construction must be convenient for being transported to the zone of reconstruction and positioned there, as well as not producing any injurious effect upon the surrounding tissues in the course of implantation and further functioning. One state-of-the-art hollow tubular stent is known to have end portions and a surface formed by a plurality of intersecting elastic elements at least part of which are interconnected at the stent ends. The stent can be of two different diametrical dimensions due to radial deformation of its elastic elements. Before being positioned at the place of reconstruction the stent is deformed so as to minimise its diametrical dimension. Then the stent is placed, in the deformed state, inside a transporting means by arranging it on a special setting bulb. Once the stent has been transported to the place of reconstruction the setting bulb is expanded so that the stent diameter is maximised. It is due to its rigid construction that the stent withstands the rather high pressure of the walls of the organ being prosthesized and provides a uniform distribution of the resultant stresses over the prosthesized surface. However, the stent in question features a lower elasticity due to restricted axial deformation, which affects the quality of endoprosthesizing. Another prior-art stent is known to be in the form of a hollow tubular springlike body made of a material having a shape memory effect (SME). Stents made from such a material are capable of restoring their shape upon a change in the temperature conditions. The advantages of said stent are determined by the properties of the material it is made from which provides for complete restoration of the stent shape in the zone of reconstruction, as well as the possibility of its convenient withdrawal from the organ being prosthesized upon cooling of the stent. The procedure of the stent positioning is improved, too. A variety of stent embodiments are possible. In particular, the stent may have a construction disclosed in the aforediscussed invention. Another stent is constructed as a hollow tubular element established by the coils of a wire or the turns of a strip. The construction of such a stent is more elastic since the stent is deformable both radially and axially. However, with this stent it is not always possible to provide an optimum value of the pitch of spring coils or of strip turns because with too large a pitch a uniform pressure distribution over the surface being prosthesized is affected, which may result in partial vessel stenosis. In the case of too small a pitch, stent implantation may cause hyperplasia of the intima of the vascular wall in the organ under reconstruction, as well as early thrombotic complications. Another stent from the prior art is known to appear as a three-dimensional tubular structure established by a number of interlaced rigid and elastic threads arranged in two groups along helical lines directed oppositely to each other. The ends of threads on the end faces of the tubular structure are not connected to one another, or to the threads of the helical coils and are arranged loosely (CH, A5, 662,051). The stent under consideration is elastic, easily deformable and can be placed in small-diameter delivery systems. The stent also provides for an adequate rigidity and a uniform pressure distribution over the surface being prosthesized. However, the presence of free ends of threads on the stent end faces affects adversely the framework properties as a whole. To attain the required rigidity involves increasing the number of threads used, which is undesirable since this may cause intimal hyperplasia and early thrombotic complications. Thread ends loosely arranged on the stent end faces produce an injurious effect upon the walls. In addition, more complicated systems are required for stent transfer to the place of reconstruction. Known in the present state of the art is a stent in the form of a three-dimensional structure formed by interlaced threads arranged in multistart turns of a helical line (RU, A, 1,812,980). The turns form at least two groups featuring opposite senses of the helical line. The thread is made of a material exhibiting SME. The ends of threads belonging to different groups are fixedly joined together on the end faces of the three-dimensional structure, e.g. by spot welding or splicing together. The stent under discussion provides the required rigidity and a uniform pressure distribution over the surface being prosthesized, as well as possessing elasticity. It is due to the joined together ends of threads on the stent end faces that placing the stent into a transporting system is simplified. The selected stent material ensures virtually complete restitution of its shape at the place of the prosthesis implantation. However, an artificial joining of threads results in a local change of the physical-mechanical properties of the stent, which tells negatively on the rigidity and reliability of the stent construction as a whole. Moreover, the presence of artificial joints between the threads on the stent end faces prevents attaining a maximum possible stent transformation. This in turn places a limitation on the possibility of placing the stent into small-diameter delivery systems. GB 1,205,743 discloses a surgical dilator comprising a hollow tubular member, the wall of which is provided by a tubular metal core of lattice form. The lattice core takes the form of a three-dimensional structure which may be formed by interlacing metal wires arranged in turns of a helical line. The turns form at least two groups featuring opposite senses of the helical line. The ends of the lattice core may be formed without joining, that is to say the lattice core may be made from a single wire. Summary of the Invention The object of the present invention is to provide a stent with a broad range of functional applications, possessing the required rigidity and elasticity, as well as a high degree of shape transformation. According to the present invention there is provided a stent according to claim 1. Thus, the foregoing object is attained due to the following specific features of the proposed construction: threads at the stent ends have no points of artificial joining since merging of the turns of one helical line into those of the other helical line appears as a bend of a single thread segment. Hence similar physical-mechanical properties are retained in the entire stent volume, while the sections of the thread merging at the stent ends acquire the properties of a spring and become the functionally active construction elements. The stent ends formed by all the aforementioned sections of the thread bend are capable of withstanding the pressure of the walls of the organ under reconstruction. The stent construction therefore acquires the required rigidity, so that the stent provides for a uniform pressure over the surface being prosthesized. In addition, it is due to their elastic properties that the sections of the thread bend tend to return to their original shape after having undergone deformation, thereby taking an active part in the process of the stent shape restoration. The herein-proposed stent construction features the required elasticity due to the possibility of radial and axial deformation under the action of small forces applied thereto. The stent construction provides for a high degree of transformation of the stent shape. In the case of longitudinal stent deformation the threads slide with respect to one another, with the result that the angle of their mutual arrangement changes, the stent diameter decreases and becomes equal in length. Hence the stent diameter is much reduced, whereas its length changes but insignificantly. A high degree of transformation enables different-dimension stents to be placed into a minimal diameter delivery system, a possibility that solves the problem of transporting the stent to the place of reconstruction, along both major and minor blood vessels. To attain the maximum degree of stent transformation with the required constructional rigidity remaining unaffected, the turns of all the helical lines are made of a single thread segment. Such a stent possesses high elasticity and transformation ability due to a low interlacing density and a small number of threads. In addition, low interlacing density tells positively on the quality of endoreconstruction because it reduces reaction of the walls being prosthesized to a foreign body being implanted. It is expedient in some cases that the stent features variable-pitch turns so as to provide different interlacing density along the stent length with a view to, for example, high-rate formation of the neointima of the vessel walls on individual reconstruction areas. It is possible that the stent is shaped as a three-dimensional body having a variable cross-sectional diameter along the stent length, a feature that makes it possible to obtain a stent shape adapted for endoreconstruction of defects of the various types and configurations. It is expedient that the free thread ends are joined on the surface of the three-dimensional body, to the threads that form helical turns, and/or to one another, thus adding to the stent reliability. On the sections of merging, the turns of one helical line merge into those of the helical line with the opposite sense of the helix. Thereby, the radius of curvature of the merging section is increased, and such sections become more resilient. A bend of the single thread segment on the merging sections may have various configurations, e.g. a circular arc, a loop or a U-shape. Those merging sections which are most elastic are shaped as circular arcs,having a large radius of curvature. The merging sections are arranged in different transverse planes relative to the longitudinal body axis. This makes it possible to attain a more compact arrangement of the stent ends during its transformation. It is expedient that the stent is made of a material possessing SME or a superelastic material. Such stent's possess a virtually complete degree of shape restitution. It is expedient that, with a view to reducing its thrombogenicity, in some instances the stent may be provided with a biocompatible material. Practical realisation of the specific features of the present invention imparts an important technical effect to the stent, namely that the required constructional rigidity is attained along with high elasticity and transformation ability. Practical use of the herein-proposed technical solution provides for a number of positive properties that follow: Required constructional rigidity and uniform pressure distribution over the surface being prosthesized; High stent elasticity; High degree of shape transformation, which enables the stent to be placed into minimal diameter delivery systems; Lower traumatogenicity of the stent implanting procedure; Broad range of functional applications. Brief Description of the Drawings FIG. 1 is a general view of a stent not being an embodiment of the present invention; FIG. 2 shows a stent according to the present invention, wherein the bending points of threads on the merging sections are situated on transverse planes relative to the longitudinal axis of the three-dimensional body; FIG. 3 shows another stent not being an embodiment of the present invention used as a filter; FIG. 4 shows a stent not being an embodiment of the present invention aimed at endoreconstruction of perforating defects; and FIG. 5 shows a stent not being an embodiment of the present invention aimed at endoreconstruction of aneurysms vessels. Referring now to the accompany drawings, FIG. 1 presents a stent appearing as a three-dimensional body made of interlaced elastic threads 1 arranged in multistart turns along a helical line in two groups, 2 and 3, featuring opposite senses of helix. The stent is made of a single segment of the thread 1 whose loose ends 4 are joined together and to the threads 1 of the groups 2 and 3 by interlacing. The stent ends, defined by sections 5, are formed by merging the turns of the thread 1 of the group 2 into the turns of the thread 1 of the group 3 and appear as a bend of the single segment of the thread 1. The bend of the thread 1 in section 5 is shaped as a circular arc. FIG. 2 presents a stent according to the invention wherein the bending points of the threads 1 in the merging sections 5 are situated in different transverse planes, a1, a2 and b1, b2 with respect to the longitudinal stent axis and are arranged in an alternating order. The bends of the threads 1 in the merging sections 5 are shaped as circular arcs. The stent is made from a single segment of the thread 1. Such a stent is preferable for large-diameter stents used in, for example, endoprosthesizing the aorta, when a minimal diameter of the stent ends is to be provided in the deformed state with the required rigidity of the stent construction remaining unaffected. The diameter of this stent can be reduced more than tenfold throughout its entire length. The number of turns of the thread 1 and their pitch are predetermined from the required interlacing density, which is so selected that the area S of meshes established by the intersecting helical turns provides the required rigidity, whereas the meshes should be large enough not to cause hyperplasia of the intima of the walls under reconstruction or earlier thromboses complications. FIG. 3 presents a stent, wherein the cross-sectional diameter in the central portion of the three-dimensional body is much larger than the cross-sectional diameters of the stent ends. The stent is spherically-shaped and is aimed at use as a filter, for example, preventing thromboembolism of the pulmonary artery. The merging sections 5 at the stent ends are loop-shaped. FIG. 4 presents a stent intended for reconstruction, examples of which are repairing perforating injuries of the cardiac septa, or the open arterial duct. The stent has a minimum transverse diameter at the centre of the three-dimensional body and a maximum possible transverse diameter at its ends. The stent dimensions are selected so that the length exceeds the maximum diameter of a defect 6, and the diameter of the stent ends is such that the projection of the stent ends onto a wall 7 exceeds the area of the defect 6. The dotted line indicates the shape assumed by the stent in the strained state. The stent is positioned in the strained state through a perforation of the defect 6. Once in position the stent resumes its original shape, whereby its end portions open up to their maximum diameter and are fixed outside the defect 6. FIG. 5 presents a stent embodiment applicable in the case of an aneurysmal dilation of a blood vessel. The stent is provided with additionally interwoven threads 1 in a section 8, which features a higher interlacing density of threads 1. This results in an accelerated neointima formation and in the exclusion of an aneurysmal cavity 9 from the blood stream along a vessel 10. The herein-proposed stent operates as follows. A preliminary catheterization of the afferent passages is performed under aseptic conditions. A guide wire is inserted into the catheter, and the guide wire working end is placed outside the zone of reconstruction. Then the catheter is withdrawn, whereupon the stent and the delivery system are fitted in succession onto the free guide wire end, said delivery system appearing as two coaxial catheters. Next the stent is deformed by applying slight longitudinal forces to the stent ends, after which the strained stent is placed into the free space of the outside catheter of the delivery system. Subsequently the assembled delivery system is brought to the place of endoreconstruction under fluoroscopy and is released. The stent assumes its original shape and is fixed reliably in position. Thus, the stent construction provides for its quick and convenient implantation in the zone of reconstruct ion. Industrial Applicability The proposed invention is instrumental in attaining high-quality reliable endoprosthesizing of blood vessels, ducts, and perforating defects of various organs, which is confirmed by good clinical effects attained in implantation of the stents in cases of occlusion-stenotic pathology of blood vessels, vascular aneurysms, obstructions of the billiary ducts, and in portal hypertension (TIPS). The aforelisted surgeries were conducted in St.Petersburg in 1992 - 1994 on the basis of the Central Roentgenology and Radiology Research Institute, the St.Petersburg State Medical Academy, as well on the basis of the Central Regional Clinical Hospital.

Claims: A stent shaped as a three-dimensional body with a longitudinal axis having a surface formed by at least two groups of turns (2, 3) of an interlaced single length of an elastic thread (1) arranged along helical lines having opposite senses of helix, the three-dimensional body having end faces formed by sections (5) where the turns of one helical line pass into the turns of the other helical line, each section (5) being formed by a bend of the single length of elastic thread (1) from which the turns of the helical lines are made, characterised in that the bends at each end face where the turns of one helical line pass into the turns of the other helical line are situated in different transverse planes (al, a2; bl, b2) relative to the longitudinal axis of the three-dimensional body. A stent as claimed in Claim 1, wherein the turns (2, 3) are of variable pitch. A stent as claimed in Claim 1 or Claim 2, wherein the three-dimensional body has a variable transverse diameter. A stent as claimed in any one of Claims 1 to 3, wherein only a predetermined portion (8) of the three-dimensional body is provided with additionally interwoven threads. A stent as claimed in any one of Claims 1 to 4, wherein the thread (1) is made of a material having shape memory effect. A stent as claimed in any one of Claims 1 to 4, wherein the thread (1) is made of a superelastic material. A stent as claimed in any one of Claims 1 to 6, wherein the three-dimensional body has a coating of biocompatible material. A stent as claimed in any one of Claims 1 to 7, wherein the groups of turns (2, 3) are adapted to slide with respect to one another.

Inventors: KAREV ANDREI VLADIMIROVITCH, PULNEV SERGEI APPOLONOVICH, SCHUKIN SERGEI VLADIMIROVITCH, KAREV, ANDREI VLADIMIROVITCH, PULNEV, SERGEI APPOLONOVICH, SCHUKIN, SERGEI VLADIMIROVITCH, KAREV, ANDREI VLADIMIROVICH, SCHUKIN, SERGEI VLADIMIROVICH
Applicants: KAREV ANDREI VLADIMIROVICH, PULNEV SERGEI APPOLONOVICH, SCHUKIN SERGEI VLADIMIROVICH, KAREV, ANDREI VLADIMIROVICH, PULNEV, SERGEI APPOLONOVICH, SCHUKIN, SERGEI VLADIMIROVICH
Application year: 1994
Main classification: A61F2
IPC codes: A61B17, A61F2